The present invention is directed to a method and apparatus for attaching a first component to a second component. More particularly, the invention is directed to such a method which comprises inserting a depending portion of the first component at least partially into a bore of the second component and then evacuating the bore to create a pressure differential across the first component which will force the depending portion into the bore to thereby attach the first component to the second component. In one illustrative embodiment, the present invention is directed to a method and apparatus for installing a tree cap on a subsea christmas tree using a remotely operated vehicle (“ROV”).
A prior art method for installing a tree cap on a subsea christmas tree is described in U.S. Pat. No. 5,992,526, which is commonly owned herewith. In this patent, the tree cap comprises a seal plate which is adapted to seal within a bore of the tree, a hydraulic setting piston which drives the seal plate downwardly into the bore, and a hydraulic lockdown piston which forces a lockdown ring into engagement with the inner diameter of the tree to thereby lock the tree cap to the tree. However, in order to accommodate the hydraulic setting and lockdown pistons, the tree cap must be provided with corresponding piston chambers and conduits for connecting the piston chambers to a source of hydraulic fluid, and this necessarily increases the size, weight and complexity of the tree cap.
Furthermore, the downward forces on the seal plate and the lockdown piston create upwardly directed reaction forces on the tree cap which must be countered to prevent the tree cap from being pushed off the tree. In the aforementioned patent, these reaction forces are countered by providing the tree cap with a pair of inwardly biased latch pins which engage corresponding grooves formed on the outer diameter of the tree. However, requiring the tree cap to be latched to the outer diameter of the tree increases the size, weight and complexity of the tree cap. Such a requirement also necessitates the additional step of disengaging the latch pins prior to retrieving the tree cap.